<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .box1{
            width: 100vw;
            height: 1000px;
            background: yellow;
        }
        .box2{
            width: 100%;
            height: 1000px;
            background: red;
        }
    </style>
</head>
<body>
    <div class="box1"></div>
    <div class="box2"></div>

    <!-- 
        没有滚动条时
        100vw === 100%
        有滚动条
        100vw  包含滚动条，窗口大小
        100%    刨除滚动条 剩余的空间占满
     -->
</body>
</html>